Method and apparatus for laser scribing glass sheet substrate coatings

ABSTRACT

A method and apparatus for laser scribing coatings on glass sheet substrates.

CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.10/425,704 filed on Apr. 30, 2003, now U.S. Pat. No. 6,919,530 which isa continuation of U.S. patent application Ser. No. 09/928,203 filed onAug. 10, 2001, now U.S. Pat. No. 6,559,411, each of which isincorporated by reference in its entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under NREL SubcontractNo. ZAX-8-17647-06, Prime Contract No. DE-AC36-98GO10337 awarded by theDepartment of Energy. The government has certain rights in thisinvention.

TECHNICAL FIELD

This invention relates to a method and an apparatus for laser scribingof coated layers on glass sheet substrates.

BACKGROUND

Laser scribing of coated layers on glass sheet substrates has been donefor many years as disclosed by U.S. Pat. No. 4,292,092 Hanak. To a largeextent, the laser scribing is performed by a laser beam that is directedfrom the coated side of the substrate; however, the scribing has alsobeen performed by directing the laser beam through the glass sheetsubstrate to the coated layers to be scribed such as disclosed by U.S.Pat. No. 4,568,409 Caplan, U.S. Pat. No. 4,854,974 Carlson et al., U.S.Pat. No. 4,892,592 Dickson et al., U.S. Pat. No. 5,296,674 Praschek etal., and U.S. Pat. No. 5,593,901 Oswald et al.

Traditional laser processing systems are of two types. One type includesa fixed laser head mounted over a movable XY table (two axis) on whichthe coated glass sheet is supported for the scribing, while the othertype includes a single axis movable laser scanning head mounted over asingle axis movable table. The major drawback of the first type is thespeed limitation of large XY tables, which is generally in the range ofabout 300 to 500 millimeters per second. Thus, in order to achievecommercially practical output, it is necessary to use multiple lasers orsplit beams to feed several laser nozzles. In addition to beingexpensive, such systems require maintaining optical alignment which isdifficult and also require that the power to each nozzle beindependently controlled. In addition, it is imperative to have realtime spacing and adjustment between nozzles to facilitate the spacingbetween scribes. The other system also has the same problems since it isdifficult to move the laser head faster than about 700 to 800millimeters per second.

Other laser scribing patents noted during an investigation conducted inconnection with the present application include U.S. Pat. No. 4,603,470Yamazaki, U.S. Pat. No. 4,689,874 Nishiura, and U.S. Pat. No. 5,956,572Kidoguchi et al.

SUMMARY

An object of the present invention is to provide an improved method forlaser scribing glass sheet substrate coatings at a relatively high speedso as to thereby provide a cost effective product.

In carrying out the above object, the method for laser scribing isperformed with a glass sheet substrate having oppositely facing surfacesone of which is uncoated and the other of which is coated. The coatedsubstrate is conveyed along a direction of conveyance adjacent a lasersource that provides a pulsed laser beam with a wavelength at anear-infrared fundamental frequency and having a pulse frequency in therange of 50 to 100 kilohertz and a pulse duration in the range of 8 to70 nanoseconds. The pulsed laser beam is reflected from the laser sourceby an XYZ galvanometer controlled mirror system toward the uncoatedsurface of the glass sheet substrate for passage therethrough to thecoating on the other surface to provide overlapping ablations throughthe coating and scribing thereof at a speed of at least 1000 millimetersper second.

The glass sheet substrate is conveyed in a vertical orientation and ispositioned laterally with respect to the direction of conveyance by gaspressure and vacuum positioners located upstream and downstream alongthe direction of conveyance from the location at which the pulsed laserbeam passes through the substrate such that the positioners control theplanarity of the substrate. The gas pressure and vacuum positionersposition the glass sheet substrate at its uncoated surface so there isno degradation of the coated surface.

Laser detectors detect the exact position of the coated substrate so thescribing laser beam can be properly focused.

In one practice of the method, the conveyance of the coated glass sheetsubstrate is provided by indexing thereof with the substrate being heldstationary during the laser scribing.

In another practice of the method, the laser scribing is performed asthe coated glass sheet substrate is conveyed.

In performing the laser scribing method, the coated glass sheetsubstrate is disclosed as having a plurality of different coated layersand a plurality of the laser scribes are made at different power levelsso the scribes extend through different layers. More specifically, inthe most rapid performance of the laser scribing method, a plurality oflaser sources and associated XYZ galvanometer controlled mirror systemsrespectively provide the pulsed laser scribing of the different scribesat different power levels, each with a wavelength at a near-infraredfundamental frequency and with pulse frequencies in the range of 50 to100 kilohertz and pulse durations in the range of 8 to 70 nanosecondsand at scribing speeds of at least 1000 millimeters per second.

Another object of the present invention is to provide improved apparatusfor laser scribing a coating on a glass sheet substrate.

In carrying out the immediately preceding object, the apparatus of theinvention includes a conveyor for conveying a glass sheet substratealong a direction of conveyance with the substrate having oppositelyfacing surfaces one of which is uncoated and the other of which has acoating. A laser source provides a pulsed laser beam with a wavelengthat a near-infrared fundamental frequency and having a pulse frequency inthe range of 50 to 100 kilohertz and a pulse duration in the range of 8to 70 nanoseconds. An XYZ galvanometer controlled mirror system reflectsthe pulsed laser beam from the laser source toward the uncoated surfaceof the glass sheet substrate for passage therethrough to the coating onthe other surface to provide overlapping ablations through the coatingand scribing thereof at a speed of at least 1000 millimeters per second.

The apparatus supports the substrate in a vertical orientation andincludes gas pressure and vacuum positioners located upstream anddownstream along the direction of conveyance from the location at whichthe pulsed laser beam passes through the substrate such that thepositioners control the planarity of the subtrate during the laserscribing.

The apparatus includes laser detectors that detect the exact position ofthe coated substrate so the scribing laser beam can be properly focused.

The apparatus disclosed includes a plurality of the pulsed laser sourcesthat operate at different power levels, each with a wavelength at anear-infrared fundamental frequency and with a pulse frequency in therange of 50 to 100 kilohertz and a pulse duration in the range of 8 to70 nanoseconds, and a plurality of XYZ galvanometer controlled lasermirror systems of the apparatus respectively reflect the pulsed laserbeams from the laser sources to provide scribing at speeds of at least1000 millimeters per second.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of various stations of a photovoltaic panelmanufacturing system that includes laser scribing apparatus constructedin accordance with the present invention to perform the method of theinvention.

FIG. 2 is a plan view of a photovoltaic panel that has been scribed toprovide separate cells.

FIG. 3 is a sectional view taken through a glass sheet substrate whichhas coated layers thereon to be scribed to provide the photovoltaicpanel.

FIG. 4 is a sectional view similar to FIG. 3 illustrating the panelafter first and second scribes have been made.

FIG. 5 is a sectional view similar to FIG. 4 illustrating the panel at alater stage after a third scribe has been made.

FIG. 6 is a schematic view that illustrates the manner in which thescribing is performed.

FIG. 7 is a view taken in the direction of line 7-7 in FIG. 6 toillustrate the construction of positioners utilized to locate the glasssheet substrate during the scribing.

FIG. 8 is a side elevational view illustrating the laser scribingstations, each of which has a right loading end, a center laser scribingmodule, and a left unloading end.

FIG. 9 is a top plan view taken at an enlarged scale along the directionof line 9-9 in FIG. 8 to illustrate the laser scribing module.

FIG. 10 is a side elevational view taken along the direction of line10-10 in FIG. 9 to illustrate the laser scribing module at an enlargedscale from that shown in FIG. 8.

FIG. 11 is a schematic view illustrating the manner in which overlappingablations through a coating on the substrate perform laser scribing.

FIG. 12 is a view illustrating one way in which the laser scribingproceeds by conveying indexes with the laser scribing performed as thecoated glass sheet substrate is held stationary.

FIG. 13 is a view of another way in which the laser scribing proceeds bycontinuously moving the coated glass sheet substrate and moving thelaser beam angularly along the direction of conveyance.

DETAILED DESCRIPTION

With reference to FIGS. 1, 2 and 3 of the drawings, a system 20 includescertain illustrated stations utilized in manufacturing of a photovoltaicpanel 22. The panel 22 is manufactured using a glass sheet substrate 24which is shown in FIG. 3 as having one surface coated with a tin oxidelayer 26. After washing and cleaning of the tin oxide coated glasssubstrate 24, a cadmium sulfide layer 28 about 3000 angstroms thick isdeposited at a first station 30. The manufacturing proceeds as the glasssheet substrate is conveyed along a direction of conveyance illustratedby arrow C to a second station 32 where a cadmium telluride layer 34about 3 microns thick is deposited prior to movement through treatingstations 36 and 38. After subsequent conveyance of the substrate to afirst scribing station 40, pulsed laser scribing apparatus 42 _(a)provides scribing of a first set of scribes 44, in a manner performed inaccordance with the present invention as is hereinafter more fullydescribed, through the tin oxide layer 26, the cadmium sulfide layer 28and the cadmium telluride layer 34. After scribing the first set ofscribes 44, the substrate is then conveyed to a station 46 where thefirst set of scribes 44 are filled with a dielectric material 48,whereupon the substrate is conveyed to a second scribing station 50where pulsed laser scribing apparatus 42 _(b) constructed in accordancewith the invention operates at a lower power level than the firstscribing station to provide scribing of a second set of scribes 52through the cadmium sulfide layer 28 and the cadmium telluride layer 34without scribing the tin oxide layer 26. The substrate is then conveyedto a coating station 54 where an electrically conductive back contactlayer 56 (FIG. 5) is applied prior to movement to a treatment station58. The substrate is then conveyed to a third scribing station 60 wherescribing apparatus 42 _(c) constructed in accordance with this inventionoperates at a lower power level than the second scribing station toprovide a third set of scribes 62 through the back contact layer 56 inorder to provide separate cells 64 that are electrically connected toeach other in series. Electrical connectors 65 shown in FIG. 2 provideelectrical connection of the panel for use.

The deposition of the cadmium sulfide at station 30 illustrated in FIG.1 and the deposition of the cadmium telluride at station 32 may beperformed in accordance with the disclosures of U.S. Pat. No. 5,248,349Foote et al., U.S. Pat. No. 5,372,646 Foote et al., U.S. Pat. No.5,470,397 Foote et al., U.S. Pat. No. 5,536,333 Foote et al., U.S. Pat.No. 5,934,163 Powell et al., and U.S. Pat No. 6,037,241 Powell et al.,the entire disclosures of which are hereby incorporated by reference.

The photovoltaic panel 22 shown in FIG. 2 has an elongated shape with awidth of about 60 centimeters (600 millimeters) between its oppositesides 66 and a length of about 120 centimeters between its opposite ends68. Furthermore, the scribing described above provides 115 of the cells64 such that the available space for each cell including the associatedscribes is just slightly more than one centimeter. Each set of scribesfor providing the 115 cells of the panel thus has a total length ofabout 69,000 millimeters. In order to perform economical manufacturingwhere the panels can be made in about a minute or so, the laserapparatus must have a scribing speed of about 1000 millimeters persecond or greater. In actuality, the scribing apparatus of the inventionas is hereinafter more fully described has a scribe speed of 2000 to3000 millimeters per second to allow for transfer time between stations.While it is possible to utilize a single laser apparatus to do each setof scribes, provision of the laser scribing apparatus 42 _(a), 42 _(b),and 42 _(c) at each of the three scribing stations as illustrated inFIG. 1 provides a higher rate of operation and a consequently more costefficient product.

The method for laser scribing coated glass sheet substrates will bedescribed in connection with the laser scribing apparatus 42 in anintegrated manner to facilitate an understanding of all aspects of theinvention. This laser scribing apparatus 42 is illustrated in FIGS. 6-10and as specifically illustrated in FIG. 8 includes a right loading end70, a left unloading end 72, and a central laser scribing module 74. Thecoated glass sheet substrate to be scribed is conveyed in a verticallyextending orientation toward the left from the loading end 70 to thelaser scribing module 74 for the laser scribing and is subsequentlyconveyed toward the left to the unloading end 72 in preparation fordelivery to the next station. The conveyance from the loading end 70 isprovided on a loading cart 76 and the glass sheet is received by a laserscribing conveyor 78 best shown in FIG. 10 for accurately controlledconveyance during the laser scribing operation. After the laser scribingas is hereinafter more fully described, the scribed glass sheetsubstrate is delivered from the laser scribing conveyor 78 to anunloading cart 80 of the unloading station 72 shown in FIG. 8. Theconveyor 78 conveys the glass sheet substrate 24 which as illustrated inFIG. 6 has an uncoated surface 81 and a coated surface 82 on which thetin oxide, cadmium sulfide and cadmium telluride layers are located suchthat this would correspond to scribing at the first scribing station 40illustrated in FIG. 1 prior to application of the back contact layerpreviously described. The scribing is performed by directing a laserbeam through the glass sheet substrate 24 from its uncoated surface 81to its coated surface 82 and through to the different layers for thescribing, with the layers scribed being controlled by the power level ofthe laser for each of the scribes.

As best illustrated in FIG. 9, the laser scribing apparatus 42 includesa laser source 83 that provides the pulsed laser beam 84 with awavelength at a near-infrared fundamental frequency and having a pulsefrequency in the range of 50 to 100 kilohertz and a pulse duration inthe range of 8 to 70 nanoseconds. The specific laser source 83 utilizedis a diode-pumped, Q-switched, neodymium-doped, yttrium vanadate lasersource providing a pulsed laser beam with a wavelength at itsnear-infrared fundamental frequency of 1064 nanometers and operating ata pulse frequency in the range of 50 to 100 kilohertz with the pulseduration in the range of 8 to 70 nanoseconds. The pulsed laser beam isreflected by mirrors 86 and 88 to an XYZ galvanometer controlled mirrorsystem collectively indicated by 90 that directs the laser beam toperform the scribing. More specifically, the XYZ galvanometer controlledmirror system 90 includes a galvanometer controlled focuser 92 thatmoves a lens horizontally to control the focal length of the beam in theZ direction and a galvanometer controlled dual mirror assembly 94 thatdirects the beam in the XY directions so as to thereby collectivelyprovide XYZ control.

By laser scribing of the scribes from the uncoated surface 81 of theglass sheet substrate 24 shown in FIG. 6, there is no gas plume formedby the ablations that provide the scribing such that the plumes cannotprevent the next laser pulses from passing through the coatings toprovide each next ablation. More specifically, the scribing as shown inFIG. 11 is performed with the ablations 95 overlapping each other. Anoverlap of 50% provides a generally uniform scribe width and a fastscribe speed. The ablations 95 thus provide a scribe such as the firstscribe 44 illustrated in FIG. 11, and the second and third scribes arealso provided in the same way.

With continuing reference to FIG. 6 and additional reference to FIG. 10,the laser scribing apparatus 42 includes gas pressure and vacuumpositioners 96 that maintain the glass sheet substrate planar at itsuncoated surface 81 and position the substrate laterally with respect tothe direction of conveyance so the focused pulsed laser beam has itsfocus in the Z direction at the layer or layers being scribed. Thesepositioners 96 are located in vertically extending sets both upstreamand downstream of the location where the laser beam 84 passes throughthe glass sheet substrate to provide the laser scribing. Morespecifically as illustrated in FIG. 10, there are five of thepositioners 96 upstream of the scribing location and five of thepositioners downstream of the scribing location. As illustrated in FIGS.6 and 7, each of the positioners 96 has a central location 98 to which avacuum is applied from a vacuum source 100 through an associated conduit102. An annular porous member 104 of each positioners 96 extends aroundthe central location 98 and receives pressurized gas from a gas source106 through an associated conduit 108. The positioners 96 position theuncoated glass sheet surface 81 within about 4-6 microns so as toprovide an accurate location for the laser beam focusing and theablations at the layer or layers being scribed.

As shown in FIGS. 6, 8 and 10, laser detectors 109 located upstream fromthe scribing location provide laser detection beams 109 _(a) (FIG. 6)that are reflected back from the uncoated glass surface 81 to detect theexact position of the glass substrate and through connection to thefocuser of the galvanometer mirror system 90 focuses the pulsed scribinglaser beam 84 in response to the position detected throughout the rangeof movement and scribing of the scribing laser beam. This detectionaccommodates for any nonplanarity of the glass sheet substrate such asroller waves formed when the glass is manufactured.

Two different ways in which the laser scribing can be performed arerespectively illustrated in FIGS. 12 and 13. In FIG. 12, the laserscribing station conveyor provides a conveying index 110 between eachlaser scribe 112 during which the coated substrate is held stationarysuch that the laser beam moves vertically to perform the scribing, afterfirst having been adjusted horizontally to provide the proper spacingbetween the previously formed adjacent scribe. As illustrated in FIG.13, it is also possible for the coated glass sheet substrate to becontinuously conveyed along the direction of conveyance C and the pathof the laser scribes 114 is then angular both along the direction ofconveyance and with respect to a true vertical direction, and after thecompletion of each scribe, there is a reset motion 115 of thegalvanometer controlled mirror system such that the complete pass asillustrated has a generally bow tie configuration.

With reference to FIG. 10, prior to conveyance to the first scribingstation, the two upper corners of the coated glass sheet substrate arelaser marked with respective fiducials which are detected by a pair ofcameras 116 so as to provide a signal for accurate location of the paneland the spacing between the fiducials so that the scribing can beaccurately located. This allows adjustment as necessary for thermalexpansion or contraction and for different spacings between thefiducials on different substrates.

In addition, each substrate can be provided with a bar code that issensed by a bar code reader 118 shown in FIG. 9 so as to provideidentification of each particular substrate being scribed. In addition,the apparatus includes an exhaust hood 120 that receives the exhaustfrom the coated side of the substrate being scribed. To insure that thescribing is performed at the proper power level, the galvanometercontrolled mirror 90 can periodically reflect the laser beam as shown at84 _(a) to a power meter 122 whose sensed power can then be utilized toprovide any necessary adjustment of the power level from the pulsedlaser source 83.

In order to provide the first, second and third sets of scribes 44, 52and 62 through the different layers as described above, the averagepower levels of the lasers are respectively about 20 watts, 8 to 9watts, and 4 to 5 watts.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternatives for practicing the invention as definedby the following claims.

What is claimed is:
 1. A method for laser scribing comprising: scribing a glass sheet substrate having an uncoated surface and a coated surface including a tin oxide layer, a cadmium sulfide layer and a cadmium telluride layer by passing a first laser beam generated by a laser source configured to provide a beam having a wavelength capable of scribing the tin oxide layer, the cadmium sulfide layer and the cadmium telluride layer through the uncoated surface of the glass sheet substrate and passing a second laser beam generated by a laser source capable of scribing the cadmium sulfide layer and the cadmium telluride layer without scribing the tin oxide layer through the uncoated surface of the glass sheet substrate, and further comprising conveying the glass sheet substrate such that the glass sheet substrate is conveyed in a vertical orientation and moves horizontally during processing. 